<p>给定一棵二叉树 <code>root</code>，返回所有<strong>重复的子树</strong>。</p>

<p>对于同一类的重复子树，你只需要返回其中任意<strong>一棵</strong>的根结点即可。</p>

<p>如果两棵树具有<strong>相同的结构</strong>和<strong>相同的结点值</strong>，则它们是<strong>重复</strong>的。</p>

<p>&nbsp;</p>

<p><strong>示例 1：</strong></p>

<p><img alt="" src="https://assets.leetcode.com/uploads/2020/08/16/e1.jpg" style="height: 236px; width: 300px;" /></p>

<pre>
<strong>输入：</strong>root = [1,2,3,4,null,2,4,null,null,4]
<strong>输出：</strong>[[2,4],[4]]</pre>

<p><strong>示例 2：</strong></p>

<p><img alt="" src="https://assets.leetcode.com/uploads/2020/08/16/e2.jpg" style="height: 125px; width: 200px;" /></p>

<pre>
<strong>输入：</strong>root = [2,1,1]
<strong>输出：</strong>[[1]]</pre>

<p><strong>示例 3：</strong></p>

<p><strong><img alt="" src="https://assets.leetcode.com/uploads/2020/08/16/e33.jpg" style="height: 202px; width: 300px;" /></strong></p>

<pre>
<strong>输入：</strong>root = [2,2,2,3,null,3,null]
<strong>输出：</strong>[[2,3],[3]]</pre>

<p>&nbsp;</p>

<p><strong>提示：</strong></p>

<ul>
	<li>树中的结点数在<code>[1,10^4]</code>范围内。</li>
	<li><code>-200 &lt;= Node.val &lt;= 200</code></li>
</ul>
